Method and apparatus for coupling to regions in an optical modulator

ABSTRACT

An optical switch having regions to which conductors are coupled outside an optical path of the optical switch. In one embodiment, the disclosed optical switch includes a plurality of first polarity regions arranged along an optical waveguide disposed in a semiconductor substrate layer. A first polarity region signal line conductor is in contact with each one of the plurality of first polarity regions outside an optical path of the optical waveguide. A plurality of second polarity regions are arranged along the optical waveguide disposed in the semiconductor substrate layer. A second polarity region signal line conductor is in contact with each one of the plurality of second polarity regions outside the optical path of the optical waveguide.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the switching signalsand, more specifically, the present invention relates to switching ormodulating optical signals.

[0003] 2. Background Information

[0004] The need for fast and efficient optical switches is increasing asInternet data traffic growth rate is overtaking voice traffic pushingthe need for optical communications. Two commonly found types of opticalswitches are mechanical switching devices and electro-optic switchingdevices.

[0005] Mechanical switching devices generally involve physicalcomponents that are placed in the optical paths between optical fibers.These components are moved to cause switching action. Micro-electronicmechanical systems (MEMS) have recently been used for miniaturemechanical switches. MEMS are popular because they are silicon based andare processed using somewhat conventional silicon processingtechnologies. However, since MEMS technology generally rely upon theactual mechanical movement of physical parts or components, MEMS aregenerally limited to slower speed optical applications, such as forexample applications having response times on the order of milliseconds.

[0006] In electro-optic switching devices, voltages are applied toselected parts of a device to create electric fields within the device.The electric fields change the optical properties of selected materialswithin the device and the electro-optic effect results in switchingaction. Electro-optic devices typically utilize electro-opticalmaterials that combine optical transparency with voltage-variableoptical behavior. One typical type of single crystal electro-opticalmaterial used in electro-optic switching devices is lithium niobate(LiNbO₃).

[0007] Lithium niobate is a transparent, material that exhibitselectro-optic properties such as the Pockels effect. The Pockels effectis the optical phenomenon in which the refractive index of a medium,such as lithium niobate, varies with an applied electric field. Thevaried refractive index of the lithium niobate may be used to provideswitching. The applied electrical field is provided to present dayelectro-optical switches by external control circuitry.

[0008] Although the switching speeds of these types of devices are veryfast, for example on the order of nanoseconds, one disadvantage withpresent day electro-optic switching devices is that these devicesgenerally require relatively high voltages in order to switch opticalbeams. Consequently, the external circuits utilized to control presentday electro-optical switches are usually specially fabricated togenerate the high voltages and suffer from large amounts of powerconsumption. In addition, integration of these external high voltagecontrol circuits with present day electro-optical switches is becomingan increasingly challenging task as device dimensions continue to scaledown and circuit densities continue to increase. These devices also tendto have large insertion losses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention is illustrated by way of example and notlimitation in the accompanying figures.

[0010]FIG. 1 is a side view illustration of one embodiment of an opticalswitch including an optical switching device having conductors coupledto regions outside an optical path in accordance with the teachings ofthe present invention.

[0011]FIG. 2 is a top view illustration of one embodiment of an opticalswitch including an optical switching device having conductors coupledto regions outside an optical path in accordance with the teachings ofthe present invention.

[0012]FIG. 3 is a top view illustration of another embodiment of anoptical switch including an optical switching device having conductorscoupled to regions outside an optical path in accordance with theteachings of the present invention.

[0013]FIG. 4 is a perspective view illustration of one embodiment of anoptical switch including an optical rib waveguide having regions towhich conductors are coupled outside an optical path in accordance withthe teachings of the present invention.

[0014]FIG. 5 is a perspective view illustration of another embodiment ofan optical switch including an optical rib waveguide having regions towhich conductors are coupled outside an optical path in accordance withthe teachings of the present invention.

DETAILED DESCRIPTION

[0015] Methods and apparatuses for switching or modulating an opticalbeam in an optical switch are disclosed. In the following descriptionnumerous specific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone having ordinary skill in the art that the specific detail need notbe employed to practice the present invention. In other instances,well-known materials or methods have not been described in detail inorder to avoid obscuring the present invention.

[0016] Reference throughout this specification to “one embodiment” or“an embodiment” means that a particular feature, structure orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment. Furthermore, the particular features, structuresor characteristics may be combined in any suitable manner in one or moreembodiments.

[0017] In one embodiment of the present invention, a semiconductor-basedoptical switch or modulator is provided in a fully integrated solutionon a single integrated circuit chip. One embodiment of the presentlydescribed optical switch includes an optical rib waveguide disposed in asemiconductor substrate and can be used in a variety of high bandwidthapplications including multi-processor, telecommunications, networkingor the like.

[0018] In one embodiment, conductors or signal lines are coupled to orare in contact with regions of the optical rib waveguide outside anoptical path in accordance with the teachings of the present invention.In one embodiment, the presently described optical switching device isused to modulate an optical beam and includes an array of trenchcapacitors disposed in an optical rib waveguide in a siliconsemiconductor substrate layer. The array of trench capacitors may alsobe referred to as a phase array and may be used to switch, modulate,route, etc. an optical beam in accordance with the teachings of thepresent invention. Charge in the array is modulated by the trenchcapacitors to modulate the optical beam directed through the array inresponse to a signal.

[0019] In one embodiment, the control circuitry used to generate thesignal to modulate the optical beam is integrated in the same die as thearray. Thus, in one embodiment the array and the control circuitry arefully integrated on the same integrated circuit chip. In one embodiment,the optical beam is switched by the array selectively attenuating theoptical beam. In another embodiment, the optical beam is switched byselectively modulating the phase of at least a portion of the opticalbeam.

[0020]FIG. 1 is a side view illustration of one embodiment of an opticalswitch 101 including an optical switching device 134 disposed in asemiconductor substrate layer 103 in accordance with the teachings ofthe present invention. As will be discussed, optical switching device134 in one embodiment is disposed in an optical rib waveguide disposedbetween an optical input port 149 and an optical output port 151. In oneembodiment, there is an optical path between optical input port 149 andoptical path 151.

[0021] In one embodiment, optical switch 101 is a controlled collapsechip connection (C4) or flip chip packaged integrated circuit diecoupled to package substrate 109 through ball bonds 107. As can beappreciated by those skilled in the art, ball bonds 107 provide moredirect connections between the internal integrated circuit nodes ofoptical switch 101 and the pins 121 of package substrate 109, therebyreducing inductance problems associated with typical wire bondintegrated circuit packaging technologies. In one embodiment, theinternal integrated circuit nodes of optical switch 101 are locatedtowards the front side 104 of optical switch 101. Another characteristicof flip chip packaging is that full access to a back side 102 of opticalswitch 101 is provided. It is appreciated that in another embodiment,optical switch 101 is not limited to being mounted in a flip chippackaged configuration. In other embodiments, packaging technologiesother than flip chip packaging may be employed in accordance with theteachings of the present invention such as for example but not limitedto wire bond packaging or the like.

[0022] In one embodiment, optical switching device 134 includes an arrayof trench capacitors including trench capacitor 135 and trench capacitor137, as illustrated in FIG. 1. In one embodiment, trench capacitors 135and 137 include polysilicon disposed in a semiconductor substrate layer103 of optical switch 101. In one embodiment, semiconductor substratelayer 103 includes silicon. As illustrated in FIG. 1, one embodiment ofoptical switch 101 includes an insulating region 153 disposed betweenthe polysilicon of trench capacitor 135 and semiconductor substratelayer 103. Similarly, an insulating region 155 is disposed between thepolysilicon of trench capacitor 137 and semiconductor substrate layer103.

[0023] In one embodiment, a signal 129 and a signal′ 131 are coupled tobe received by trench capacitors 135 and 137, respectively, of opticalswitching device 134 through conductors 119 and 121, respectively. Inaddition, semiconductor substrate layer 103 in one embodiment is coupledto ground 160 through conductor 158. In one embodiment, signal 129 andsignal′ 131 are generated by control circuitry on the integrated circuitdie of optical switch 101. In one embodiment, conductors 119, 121 and158 are coupled to trench capacitors 135, 137 and semiconductorsubstrate layer 103 outside the optical path between optical input port149 and optical output port 151. Although FIG. 1 illustratessemiconductor substrate layer 103 coupled to conductor 158 in only onelocation, it is appreciated that conductor 158 may be coupled tosemiconductor substrate layer 103 in multiple locations in otherembodiments. Similarly, conductor 119 may be coupled to trench capacitor135 in multiple locations and that conductor 121 may be coupled totrench capacitor 137 in multiple locations in accordance with theteachings of the present invention.

[0024] In one embodiment, the control circuit generating signal 129 andsignal′ 131 is disposed in semiconductor substrate layer 103 outside ofthe optical path between optical input port 149 and optical port 151. Inanother embodiment, signal 129 and signal′ 131 are generated by controlcircuitry external to the integrated circuit die of optical switch 101.As shown in the embodiment of FIG. 1, trench capacitors 135 and 137 arecoupled to conductors 119 and 121, respectively, which are disposed inan optical confinement layer 105 of optical switch 101. Similarly,semiconductor substrate layer 103 is coupled to conductor 158, which isdisposed in optical confinement layer 105. In one embodiment, opticalconfinement layer 105 is an insulating layer and includes a dielectriclayer of optical switch 101.

[0025] In one embodiment, signal 129 and signal′ 131 are a plurality ofsignals separately coupled to be received by the trench capacitors 135and 137 in optical switching device 134. For example, in one embodiment,signal 129 and signal′ 131 are the same signals having oppositepolarities. In another embodiment, signal 129 and signal′ 131 are thesame signals having the same polarities. In yet another embodiment,signal 129 and signal′ 131 are separate signals coupled to capacitorsacross the array to control or modulate a charge distribution of freecharge carriers across the array of trench capacitors 135 and 137.

[0026] As illustrated in FIG. 1, optical switch 101 includes opticalinput port 149 and optical output port 151 disposed in or opticallycoupled to semiconductor substrate layer 103 on different sides of thearray of trench capacitors 135 and 137 of optical switching device 134.In one embodiment, an optical beam 111 is directed through optical inputport 149 and through semiconductor substrate layer 103 to the array oftrench capacitors 135 and 137 of optical switching device 134. As willbe discussed, one embodiment of optical switch 101 includes an opticalrib waveguide disposed in semiconductor substrate layer 103 betweenoptical input port 149 and optical output port 151 through which opticalbeam 111 and a switched optical beam 127 propagate. In one embodiment,optical beam 111 is directed into optical input port 149 through anoptical fiber or the like. As mentioned, in one embodiment,semiconductor substrate layer 103 include silicon, trench capacitors 135and 137 include polysilicon and optical beam 111 includes infrared ornear infrared laser light. As known to those skilled in the art, siliconis partially transparent to infrared or near infrared light,particularly if the free carrier doping is kept low. For instance, inone embodiment in which optical switch 101 is utilized intelecommunications, optical beam 111 has an infrared wavelength ofapproximately 1.55 or 1.3 micrometers.

[0027] As will be discussed, optical beam 111 is switched or modulatedby the array of trench capacitors 135 and 137 of optical switchingdevice 134 in one embodiment. A switched optical beam 127 is thendirected from the array of trench capacitors 135 and 137 throughsemiconductor substrate layer 103 to optical output port 151. In oneembodiment, switched optical beam 127 is directed from optical outputport 151 through an optical fiber or the like. It is appreciated that inother embodiments (not shown), optical beam 111 and switched opticalbeam 127 may enter and/or exit semiconductor substrate layer 103 throughback side 102 and/or front side 104 in accordance with the teachings ofthe present invention.

[0028] In one embodiment, optical switch 101 includes an opticalconfinement layer 157 disposed proximate to semiconductor substratelayer 103. Thus, semiconductor substrate layer 103 is disposed betweenoptical confinement layer 157 and optical confinement layer 105. In oneembodiment, optical confinement layer 157 is an insulating layer or aburied oxide layer of an SOI wafer. Optical energy or light from opticalbeam 111 or switched optical beam 127 is reflected from the interfacesbetween semiconductor substrate layer 103 and optical confinement layer157 or optical confinement layer 105. For example, light from opticalbeam 111 will have an angle of incidence θ relative to the interfacebetween semiconductor substrate layer 103 and optical confinement layer157 or optical confinement layer 105. For purposes of this disclosure,an incident angle θ is the angle that an optical beam makes with animaginary line perpendicular to a surface at the point of incidence. Inthe embodiment depicted in FIG. 1, optical beam 111 or switched opticalbeam 127 is deflected off the interface between semiconductor substratelayer 103 and optical confinement layer 157 or optical confinement layer105 because of total internal reflection.

[0029] In one embodiment, optical confinement layer 157 and opticalconfinement layer 105 include silicon oxide or the like and have anindex of refraction of approximately n_(oxide)=1.5 and semiconductorsubstrate layer 103 includes silicon and has an index of refraction ofapproximately n_(Si)=3.5. In order to have total internal reflection ofoptical beam 111 or switched optical beam 127, the incident angle θ ofoptical beam 111 or switched optical beam 127 relative to the interfacebetween semiconductor substrate layer 103 and optical confinement layer157 or optical confinement layer 105 satisfies the followingrelationship:

sin θ>n _(oxide) /n _(Si)  (Equation 1)

[0030] As a result of the total internal reflection, optical beam 111 isin one embodiment is confined to remain with semiconductor substratelayer 103 using optical confinement layer 157 and optical confinementlayer 105 until switched optical beam 127 exits through optical outputport 151.

[0031] As mentioned, one embodiment of optical switch 101 is constructedfrom an SOI wafer. In one embodiment, trench capacitors 135 and 137 arefabricated to be approximately 1-2 μm deep in semiconductor substratelayer 103. It is appreciated of course that in other embodiments, trenchcapacitors 135 and 137 may have different depths in accordance with theteachings of the present invention. Next, optical confinement layer 105is formed with conductors 119 and 131 providing accesses to trenchcapacitors 135 and 137 and conductor 158 providing access tosemiconductor substrate layer 103. Afterwards, ball bonds 107 andpackage substrate 109 are added. Conductors 119, 121 and 158 are coupledto regions of trench capacitors 135 and 137 and semiconductor substratelayer 103 outside the optical path between optical input port 149 and151. Losses in optical beam 111 and/or switched optical beam 127 arereduced in accordance with the teachings of the present invention sincea reduced amount of optical energy will be incident upon an interfacebetween conductors 119, 121 and 158 and the semiconductor material oftrench capacitors 135, 137 and semiconductor substrate layer 103.

[0032]FIG. 2 is a top view illustration of an optical switch 201including an optical switching device 234 that is biased such that anoptical beam 211 is switched in accordance with the teachings of thepresent invention. As illustrated, an optical switching device 234,including an array of trench capacitors 235, 236, 237 and 238, isdisposed in a semiconductor substrate layer 203. Insulating regions 253,254, 255 and 256 are disposed between semiconductor substrate layer 203and polysilicon of trench capacitors 235, 236, 237 and 238,respectively. In one embodiment, an optical rib waveguide providing anoptical path is disposed between optical input port 249 and opticaloutput port 251. In one embodiment, conductors (not shown) to trenchcapacitors 235, 236, 237 and 238 and semiconductor substrate layer 203are coupled to regions outside the optical path between optical inputport 249 and optical output port 251. In one embodiment, optical fibersor the like are optically coupled to optical input port 249 and opticaloutput port 251.

[0033] In one embodiment, optical confinement regions 261 and 263 aredisposed along the sides of optical path between optical input port 249and optical output port 251. In one embodiment, optical confinementregions 261 and 263 help define lateral optical confinement regions ofthe rib waveguide disposed between optical input port 249 and opticaloutput port 251. In one embodiment, optical confinement regions 261 and263 are disposed a distance D away from insulating regions 253, 254, 255and 256. In one embodiment, which is a rib waveguide embodiment, theinsulating regions 253, 254, 255 and 256 extend past the opticalconfinement regions 261 and 263, such that the distance D is less thanzero. In one embodiment, D is a distance greater than or equal to zero.Accordingly, in another embodiment in which D is equal to zero, opticalconfinement regions 261 and 263 are adjacent to insulating regions 253,254, 255 and 256. In one embodiment, the optical confinement regions 261and 263 include insulative material such as for example oxide andsemiconductor substrate layer 203 includes for example silicon. As aresult, optical beam 211 and switched optical beam 227 are confined toremain within the semiconductor substrate layer 203 until exitingthrough optical output port 251. In one embodiment, optical confinementlayers, similar to for example optical confinement layer 157 and opticalconfinement layer 105 of FIG. 1, are also disposed along the “top” and“bottom” of the optical path is disposed between optical input port 249and optical output port 251. These optical confinement layers are notshown in FIG. 2 for clarity.

[0034] In the depicted embodiment, trench capacitors 235, 236, 237 and238 are biased in response to signal voltages such that theconcentration of free charge carriers in charged regions 239, 240, 241and 242 of the array of trench capacitors is modulated. It is noted thatfor explanation purposes, charged regions 239, 240, 241 and 242 havebeen illustrated as including positive charge in the polysilicon oftrench capacitors 235, 236, 237 and 238 and negative charge in thesemiconductors substrate layer 203 across the insulating regions 253,254, 255 and 256. It is appreciated that in another embodiment, thepolarities of these charges may be reversed in accordance with theteachings of the present invention. Therefore, the polysilicon regionsof trench capacitors 235, 236, 237 and 238 may be referred to as “firstpolarity regions” and the semiconductors substrate regions ofsemiconductor substrate layer 203 between trench capacitors 235, 236,237 and 238 may be referred to as “second polarity regions” inaccordance with the teachings of the present invention.

[0035] In one embodiment in which D is greater than zero, an opticalbeam 211 is directed through semiconductor substrate layer 203 such thata portion of optical beam 211 is directed to pass through the modulatedcharge regions 239, 240, 241 and 242 and a portion of optical beam 211is not directed to pass through the modulated charge regions 239, 240,241 and 242. As a result of the modulated charge concentration incharged regions 239, 240, 241 and 242, optical beam 211 is switchedresulting in switched optical beam 227 being directed from the array oftrench capacitors through semiconductor substrate layer 203.

[0036] In one embodiment, the free charge carriers attenuate opticalbeam 211 when passing through semiconductor substrate layer 203. Inparticular, the free charge carriers attenuate optical beam 211 byabsorbing the optical beam 211 by converting some of the energy ofoptical beam 211 into free charge carrier energy.

[0037] In another embodiment, the phase of the portion of optical beam211 that passes through the charged regions 239, 240, 241 and 242 ismodulated in response to the signal. In one embodiment, the phase ofoptical beam 211 passing through free charge carriers in charged regions239, 240, 241 and 242 is modulated due to the plasma optical effect. Theplasma optical effect arises due to an interaction between the opticalelectric field vector and free charge carriers that may be present alongthe propagation path of the optical beam 211.

[0038] The electric field of the optical beam 211 polarizes the freecharge carriers and this effectively perturbs the local dielectricconstant of the medium. This in turn leads to a perturbation of thepropagation velocity of the optical wave and hence the refractive indexfor the light, since the refractive index is simply the ratio of thespeed of the light in vacuum to that in the medium. The free chargecarriers are accelerated by the field and also lead to absorption of theoptical field as optical energy is used up. Generally the refractiveindex perturbation is a complex number with the real part being thatpart which causes the velocity change and the imaginary part beingrelated to the free charge carrier absorption. The amount of phase shiftφ is given by

φ=(2π/λ)ΔnL  (Equation 2)

[0039] with the optical wavelength λ and the interaction length L. Inthe case of the plasma optical effect in silicon, the refractive indexchange An due to the electron (ΔN_(e)) and hole (ΔN_(h)) concentrationchange is given by: $\begin{matrix}{{\Delta \quad n} = {{- \frac{e^{2}\lambda^{2}}{8\pi^{2}c^{2}ɛ_{0}n_{0}}}( {\frac{{b_{e}( {\Delta \quad N_{e}} )}^{1.05}}{m_{e}^{*}} + \frac{{b_{h}( {\Delta \quad N_{h}} )}^{0\quad 8}}{m_{n}^{*}}} )}} & ( {{Equation}\quad 3} )\end{matrix}$

[0040] where n_(o) is the nominal index of refraction for silicon, e isthe electronic charge, c is the speed of light, ∈₀ is the permittivityof free space, m_(e)* and m_(h)* are the electron and hole effectivemasses, respectively, b_(e) and b_(h) are fitting parameters.

[0041] In one embodiment, the amount of phase shift φ of some portionsof optical beam 211 passing through the free charge carriers of chargedregions 239, 240, 241 and 242 is approximately π/2. In one embodiment,the phase of a portion of optical beam 211 not passing though the freecharge carriers of charged regions 239, 240, 241 and 242, i.e. passingthrough uncharged regions, is relatively unchanged. In one embodiment, aresulting interference occurs between the phase modulated portions andnon-phase modulated portions of optical beam 211 passing through thearray of trench capacitors 235, 236, 237 and 238. In one embodiment inwhich D is equal to zero, there is no portion of optical beam 211 notpassing though the free charge carriers of charged regions 239, 240, 241and 242 as optical confinement regions 261 and 263 confine optical beam211 to pass through charged regions 239, 240, 241 and 242.

[0042] It is noted that optical switch 201 has been illustrated in FIG.2 with four trench capacitors 235, 236, 237 and 238. It is appreciatedthat in other embodiments, optical switch 201 may include a greater orfewer number of trench capacitors in accordance with the teachings ofthe present invention with the number of trench capacitors chosen toachieve the required phase shift. In particular, the interaction lengthL discussed in connection with Equation 2 above may be varied byincreasing or decreasing the total number of trench capacitors 235, 236,237 and 238 in optical switching device 234 of optical switch 201.

[0043]FIG. 3 is a top view illustration of one embodiment of an opticalswitch 301 including an optical switching device 334 that is biased suchthat an optical beam 311 is switched in accordance with the teachings ofthe present invention. As illustrated, one embodiment of optical switch301 includes an optical switching device 334 having a trench capacitor335 disposed in a semiconductor substrate layer 303. An insulatingregion 353 is disposed between the polysilicon of trench capacitor 335and semiconductor substrate layer 303. In one embodiment, trenchcapacitor 335 is one of a plurality or array of trench capacitorsdisposed in semiconductor substrate layer 303. In one embodiment, anoptical rib waveguide providing an optical path is disposed betweenoptical input port 349 and optical output port 351. In one embodiment,conductors (not shown) to trench capacitor 335 and semiconductorsubstrate layer 303 are coupled to regions outside the optical pathbetween optical input port 349 and optical output port 351. In oneembodiment, optical fibers or the like are optically coupled to opticalinput port 349 and optical output port 351.

[0044] In one embodiment, optical confinement regions 361 and 363 aredisposed along the sides of optical path between optical input port 349and optical output port 351. In one embodiment, optical confinementregions 361 and 363 help define lateral optical confinement regions ofthe rib waveguide disposed between optical input port 349 and opticaloutput port 351. In one embodiment, optical confinement regions 361 and363 are disposed a distance D away from insulating region 353. In oneembodiment, D is a distance greater than or equal to zero. In oneembodiment, the optical confinement regions 361 and 363 includeinsulative material such as for example oxide and semiconductorsubstrate layer 303 includes for example silicon. As a result, opticalbeam 311 and switched optical beam 327 are confined to remain within thesemiconductor substrate layer 303 and well region 344 until exitingthrough optical output port 351. In one embodiment, optical confinementlayers, similar to for example optical confinement layer 157 and opticalconfinement layer 105 of FIG. 1, are also disposed along the “top” and“bottom” of the optical path is disposed between optical input port 349and optical output port 351. These optical confinement layers are notshown in FIG. 3 for clarity.

[0045] In the depicted embodiment, trench capacitor 335 is biased inresponse to a signal such that the concentration of free charge carriersin charged regions 339 is modulated. In an embodiment in which D isgreater than zero, an optical beam 311 is directed through semiconductorsubstrate layer 303 such that a portion of optical beam 311 is directedto pass through the modulated charge region 339 and a portion of opticalbeam 311 is not directed to pass through the modulated charge region339. As a result of the modulated charge concentration in charged region339, optical beam 311 is switched resulting in switched optical beam 327being directed from trench capacitor 335 through semiconductor substratelayer 303. In an embodiment in which D is equal to zero, there is noportion of optical beam 311 not passing through modulated charge region339.

[0046] In one embodiment, the phase of the portion of optical beam 311that passes through the charged regions 339 is modulated in response tothe signal due to the plasma optical effect discussed above. As can beobserved from Equation 2 above, one way to increase the phase shift φ inoptical beam 311 is to increase the interaction length L of the chargedregion 339. In one embodiment, an increase interaction length L isprovided by trench capacitor 335 by providing an increased dimension L,as illustrated in FIG. 3.

[0047]FIG. 4 is a perspective view illustration of one embodiment of anoptical switch 401 including an optical rib waveguide 468 having regionsto which conductors, such as for example conductors 419, 421 and 458,are coupled outside an optical path of an optical beam 411 propagatingthrough optical rib waveguide 468 in accordance with the teachings ofthe present invention. In one embodiment, conductors 419 and 421 arecoupled to apply signal 429 and signal′ 431, respectively, to regionswithin optical rib waveguide 468 as described above in connection withFIGS. 1, 2 and 3. Accordingly, in one embodiment conductors 419 and 421are coupled to first polarity regions in optical switch 401 to modulatecharge regions with the trench capacitors of optical switch 401. In oneembodiment, conductors 458 couple regions of optical rib waveguide 468to ground 460 as described above in connection with FIGS. 1, 2 and 3.Accordingly, in one embodiment conductors 458 are coupled to secondpolarity regions between trench capacitors of optical switch 401.

[0048] In one embodiment, optical rib waveguide 468 is optically coupledbetween an optical input port and an optical output port, such as forexample optical input and output port pairs 149 and 151, 249 and 251 and349 and 351 of FIGS. 1, 2 and 3, respectively. Accordingly, optical ribwaveguide 468 in one embodiment is formed in a semiconductor substratelayer such as for example semiconductor substrate layers 103, 203 or 303of FIGS. 1, 2 and 3, respectively. In one embodiment, the boundaries ofoptical rib waveguide are defined at the interfaces betweensemiconductor substrate layers 103, 203 and 303 and optical confinementlayers and/or regions 103, 157, 261, 263, 361 and 363 of FIGS. 1, 2 and3, respectively.

[0049] Referring back to the example embodiment illustrated in FIG. 4,optical rib waveguide 468 includes a rib region 462 and a slab region464. In the embodiment illustrated in FIG. 4, the intensity distributionof a single mode optical beam 411 is shown propagating through opticalrib waveguide 468. As shown, the intensity distribution of optical beam411 is such that a portion of optical beam 411 propagates through aportion of rib region 462 towards the interior to optical rib waveguide468. In addition, the majority of the optical beam 411 propagatesthrough a portion of slab region 464 towards the interior of optical ribwaveguide 468. As also shown with the intensity distribution of opticalbeam 411 in FIG. 4, the intensity of the propagating optical mode ofoptical beam 411 is vanishingly small at the “upper corners” of ribregion 462 as well as the “sides” of slab region 464.

[0050] As depicted in the embodiment shown in FIG. 4, conductor 419 isin contact with optical rib waveguide 468 in regions outside the opticalpath of optical beam 411. Similarly, conductors 421 and 458 are incontact with optical rib waveguide 468 in regions outside the opticalpath of optical beam 411. Accordingly, the propagation of optical beam411 does not reach an interface between the semiconductor substrate ofoptical rib waveguide 468 and the conductive material of conductors 419,421 and 458. This is important because the metal can absorb some portionof any electric field that impinges on it. It is appreciated that sincethe intensity of the propagating optical beam 411 is vanishingly smallat the interfaces between the semiconductor substrate of optical ribwaveguide 468 and conductive material of conductors 419, 421 and 458,the loss of the optical energy of optical beam 411 when propagatingthrough optical rib waveguide 468 is reduced.

[0051] It is noted that conductors 419, 421 and 458 are illustrated inthe embodiment of FIG. 4 as being coupled to optical rib waveguide 468in a plurality of locations throughout the comers of rib region 462 andalong the sides of slab region 464. It is appreciated that in otherembodiments, conductors 419, 421 and 458 may be coupled to other regionsof optical rib waveguide 468 outside the optical path of optical beam411 or a subset of the regions illustrated in FIG. 4 in accordance withthe teachings of the present invention. In one embodiment, conductors419, 421 and 458 are coupled to optical rib waveguide 468 through anoptical confinement layer such as for example optical confinement layer105 of FIG. 1. In another embodiment, conductors 419, 421 and 458 may becoupled to optical rib waveguide 468 through an optical confinementlayer such as for example optical confinement layer 157 of FIG. 1.

[0052]FIG. 5 is a perspective view illustration of another embodiment ofan optical switch 501 including an optical rib waveguide 568 havingregions to which conductors, such as for example conductors 519, 521 and558, are coupled outside an optical path of an optical beam 511propagating through optical rib waveguide 568 in accordance with theteachings of the present invention. Optical rib waveguide 568 is similarto optical rib waveguide 468. In one embodiment, conductors 519 and 521are coupled to apply signal 529 and signal′ 531, respectively, toregions within optical rib waveguide 568 similar to as described abovein connection with FIGS. 1, 2, 3 and 4. Accordingly, in one embodimentconductors 519 and 521 are coupled to first polarity regions in opticalswitch 501 to modulate charge regions with the trench capacitors ofoptical switch 501. In one embodiment, conductors 558 couple regions ofoptical rib waveguide 568 to ground 560 similar to as described above inconnection with FIGS. 1, 2, 3 and 4. Accordingly, in one embodimentconductors 558 are coupled to second polarity regions between trenchcapacitors of optical switch 501.

[0053] In one embodiment, optical rib waveguide 568 is optically coupledbetween an optical input port and an optical output port, such as forexample optical input and output port pairs 149 and 151, 249 and 251 and349 and 351 of FIGS. 1, 2 and 3, respectively. Accordingly, optical ribwaveguide 568 in one embodiment is formed in a semiconductor substratelayer such as for example semiconductor substrate layers 103, 203 or 303of FIGS. 1, 2 and 3, respectively. In one embodiment, the boundaries ofoptical rib waveguide are defined at the interfaces betweensemiconductor substrate layers 103, 203 and 303 and optical confinementlayers and/or regions 103, 157, 261, 263, 361 and 363 of FIGS. 1, 2 and3, respectively.

[0054] Referring back to the example embodiment illustrated in FIG. 5,optical rib waveguide 568 includes a rib region 562 and a slab region564. In the embodiment illustrated in FIG. 5, the intensity distributionof a single mode optical beam 511 is shown propagating through opticalrib waveguide 568. As shown, the intensity distribution of optical beam511 is such that a portion of optical beam 511 propagates through aportion of rib region 562 towards the interior to optical rib waveguide568. In addition, the majority of the optical beam 511 propagatesthrough a portion of slab region 564 towards the interior of optical ribwaveguide 568. As also shown with the intensity distribution of opticalbeam 511 in FIG. 5, the intensity of the propagating optical mode ofoptical beam 511 is vanishingly small at the “lower comers” of ribregion 562 as well as the “sides” of slab region 564.

[0055] As depicted in the embodiment shown in FIG. 5, conductor 519 isin contact with optical rib waveguide 568 in regions outside the opticalpath of optical beam 511 in the sides of slab regions 564 away from theinterior of optical rib waveguide 568. Similarly, conductors 521 and 558are in contact with optical rib waveguide 568 in the sides of slabregion 564 outside the optical path of optical beam 511. Accordingly,the propagation of optical beam 511 does not reach an interface betweenthe semiconductor substrate of optical rib waveguide 568 and theconductive material of conductors 519, 521 and 558. It is appreciatedthat since the intensity of propagating optical beam 511 is vanishinglysmall at the interfaces between the semiconductor substrate of opticalrib waveguide 568 and conductive material of conductors 519, 521 and558, the loss of the optical energy of optical beam 511 when propagatingthrough optical rib waveguide 568 is reduced.

[0056] It is noted that conductors 519, 521 and 558 are illustrated inthe embodiment of FIG. 5 as being coupled to optical rib waveguide 568in a plurality of locations throughout the sides of slab region 564. Itis appreciated that in other embodiments, conductors 519, 521 and 558may be coupled to other regions of optical rib waveguide 568 outside theoptical path of optical beam 511 or a subset of the regions illustratedin FIG. 5 in accordance with the teachings of the present invention. Inone embodiment, conductors 519, 521 and 558 are in contact with opticalrib waveguide 568 through an optical confinement layer such as forexample optical confinement layer 105 of FIG. 1. In another embodiment,conductors 519, 521 and 558 may be coupled to optical rib waveguide 568through an optical confinement layer such as for example opticalconfinement layer 157 of FIG. 1.

[0057] Throughout this specification, it is noted that the opticalswitching devices described in the various embodiments herein have beenillustrated using trench capacitors for discussion purposes. Inaccordance with the teachings of the present invention, appropriatelybiased trench capacitors produce an index of refraction change in thesemiconductor substrate layers in which the trench capacitors aredisposed. As discussed, the changes in index of refraction produce phaseshifts of optical beams. In some embodiments, the effects of the phaseshifts of the optical beams produce optical beam steering such thatoptical beams may be selectively directed to optical output ports inaccordance with the teachings of the present invention. It isappreciated that in other embodiments, other types of optical switchingdevices may be employed in accordance with the teachings of the presentinvention. Other known types of optical switching devices that may beemployed include for example thermal heaters, current injectors, P-Njunctions, or the like.

[0058] As is known, thermal heating of the semiconductor substrate layerin the optical beam can be employed to change the index of refraction tophase shift an optical beam. In one embodiment of the present invention,known thermal heating is accomplished in an optical switching device bydepositing thermal heaters on the surface of a semiconductor substratelayer in the form of polysilicon resistors or implanting diffusion basedresistors and passing current through these resistors. In anotherembodiment, known current injectors are employed in an optical switchingdevice for current injection to inject charge carriers into the phaseshift region of in the semiconductor substrate layer. In yet anotherembodiment, current injection is accomplished by an optical switchingdevice by using known forward biased diodes or P-N junctions disposed inthe semiconductor substrate layer. In still another embodiment, knownreverse biased P-N junctions are employed by an optical switchingdevice, which when biased cause a depletion region to be formed in thesemiconductor substrate layer. The formed depletion region causes anindex change by sweeping out charge carriers in the depletion region ofthe semiconductor substrate layer.

[0059] In the foregoing detailed description, the method and apparatusof the present invention have been described with reference to specificexemplary embodiments thereof. It will, however, be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the present invention. The presentspecification and figures are accordingly to be regarded as illustrativerather than restrictive.

What is claimed is:
 1. An apparatus, comprising: a plurality of firstpolarity regions arranged along an optical waveguide disposed in asemiconductor substrate layer; a first polarity region signal lineconductor in contact with each one of the plurality of first polarityregions outside an optical path of the optical waveguide; a plurality ofsecond polarity regions arranged along the optical waveguide disposed inthe semiconductor substrate layer; and a second polarity region signalline conductor in contact with each one of the plurality of secondpolarity regions outside the optical path of the optical waveguide. 2.The apparatus of claim 1 wherein the second polarity region signal lineconductor is coupled to provide a first potential to the plurality ofsecond polarity regions.
 3. The apparatus of claim 1 wherein the firstpolarity region signal line conductor is coupled to modulate charge inthe optical waveguide in response to a modulation signal.
 4. Theapparatus of claim 1 wherein the plurality of second polarity regionsare interspersed among the plurality of first polarity regions along theoptical waveguide disposed in the semiconductor substrate layer.
 5. Theapparatus of claim 3 further comprising first and second optical portsoptically coupled to the optical waveguide through the semiconductorsubstrate, the first optical port selectively optically coupled to thesecond optical port in response to the modulation signal.
 6. Theapparatus of claim 3 wherein the modulation signal comprises a pluralityof signals, each one of the plurality of signals coupled to be receivedby a corresponding one of the plurality of first polarity regionsoutside the optical path of the optical waveguide.
 7. The apparatus ofclaim 3 wherein the modulation signal comprises an individual signal,the individual signal coupled to be received by the plurality of firstpolarity regions outside the optical path of the optical waveguide. 8.The apparatus of claim 3 further comprising modulation signal generationcircuitry disposed in the semiconductor substrate layer, the modulationsignal generation circuitry coupled to the first polarity region signalline conductor to generate the modulation signal.
 9. The apparatus ofclaim 3 further comprising modulation signal generation circuitrydisposed in a separate semiconductor substrate layer, the modulationsignal generation circuitry coupled to the first polarity region signalline conductor to generate the modulation signal.
 10. The apparatus ofclaim 1 further comprising first and second optical confinement layersdisposed proximate to the semiconductor substrate layer, thesemiconductor substrate layer disposed between the first and secondoptical confinement layers.
 11. The apparatus of claim 1 wherein theoptical waveguide comprises a rib waveguide disposed along thesemiconductor substrate layer.
 12. A method, comprising: directing anoptical beam through an optical waveguide disposed in a semiconductorsubstrate layer; modulating charge proximate to a plurality of firstpolarity regions along the optical waveguide in response to a modulationsignal coupled to be received through a first polarity region signalline conductor in contact with each of the plurality of first polarityregions outside an optical path of the optical waveguide; coupling aplurality of second polarity regions along the optical waveguide to afirst potential through a second polarity region signal line conductorin contact with each of the plurality of second polarity regions outsidethe optical path of the optical waveguide.
 13. The method of claim 12further comprising modulating the optical beam in response to themodulation signal.
 14. The method of claim 12 further comprisingconfining the optical beam to remain within the optical waveguide whilepassing through the semiconductor substrate layer.
 15. The method ofclaim 12 wherein modulating charge proximate to the plurality of firstpolarity regions along the optical waveguide in response to themodulation signal comprises generating the modulation signal withmodulation signal generation circuitry disposed in the semiconductorsubstrate layer.
 16. The method of claim 12 wherein modulating chargeproximate to the plurality of first polarity regions along the opticalwaveguide in response to the modulation signal comprises generating themodulation signal with modulation signal generation circuitry disposedin a separate semiconductor substrate layer.
 17. An apparatus,comprising: a plurality of first polarity regions arranged along anoptical waveguide disposed in a semiconductor substrate layer; means forcoupling each of the plurality of first polarity regions to receive amodulation signal, the means for coupling each of the plurality of firstpolarity regions in contact with each of the plurality of first polarityregions outside an optical path of the optical waveguide; a plurality ofsecond polarity regions arranged along the optical waveguide disposed inthe semiconductor substrate layer; and means for coupling each of theplurality of second polarity regions to a first potential, the means forcoupling each of the plurality of second polarity regions in contactwith each of the plurality of second polarity regions outside theoptical path of the optical waveguide.
 18. The apparatus of claim 17further comprising means for generating the modulation signal coupled tothe means for coupling each of the plurality of first polarity regionsto receive the modulation signal.
 19. The apparatus of claim 17 furthercomprising optical confinement means disposed proximate to the opticalwaveguide.